Szabó János szerk.: Fragmenta Mineralogica Et Palaentologica 21. 2003. (Budapest, 2003)
lower, too, in comparison with the previously presented communities. The dominant taxon, N. fabianii, is below 50 % in both profiles. Besides N. fabianii, the second most important species is N. incrassatus (28 to 40 %). N. chavannesi (6-11 %) and N. pulchellus (7-9 %) display an eastward increase: the presence of the boreal faunal element N. aff. preshvichianus may be an indicator of the climate cooling which becomes obvious in the Early Oligocène. At the generic level, the following observations have been made. The genus Nummulites is decreasing from the West to the East, from 70 to 30 %. At Balinka, die genus Operculina overrides Nummulites (40 % against 30). Discocyclines are present in both sites in the nearly identical amounts (10-15 %), slighdy more abundant in the East. In the West, two interesting genera of larger Foraminifera appear: Chapmanina and Gyroidina in the East, the coralline red algae are important constituents of the community. The above analysis reveals that in the larger foraminifera fauna in general, and in the Nummulites fauna in particular (which arrived in the Bakony Eocene with the early Lutetian transgression), three characteristic types of communities can be distinguished. The oldest community is composed mainly of large reticulate and small punctuate Nummulites species, accompanied by a rich fauna of Alveolina. The genus Assilina is represented by the species A. spira. The next community is characterized by big punctuate and smooth Nummulites, accompanied by decreasing percentages of Assilina and Alveolina, counterbalanced by the increasing presence of discocylinids. Finally, the youngest community is characterized exclusively by small striate taxa. The boundaries of the three community types coincide with the Lutetian/Bartonian and Bartonian/Priabonian boundaries, respectively. The Bartonian/Priabonian boundary is marked also by the disappearance of Assilina, Alveolina and the extralarge Nummulites species. In the following, the factors that might have caused the changes in community types will be discussed one by one. 1 - N. fabianii, 2 - N. incrassatus, 3 - N. chavannesi, 4 - A 7 , pulchellus, 5 - N. stellatus, 6 - N. aff. preshvichianus, 7 - indet. Nummulites species Figure 6 — Geographic extension and stratigraphie position of the Nummulites communities of the Priabonian Nummulites fabianii Zone. Effects of environmental factors on palaeocommunities Included are all external factors (events, circumstances, affected also the fauna of larger foraminifera. Their study influence) that affect the formation and development of is still ongoing. Here only the hitherto recognized most communities. Several Eocene events are known which important observations and connections are reported on.
